The present invention relates to a laser obstacle detection method and sensor, and particularly to a laser obstacle detection method and sensor which can effectively prevent misdetection of an object which is not essentially an obstacle, such as raindrops, snowfall, or the like, as an obstacle, when equipped on a vehicle for detecting an obstacle in a traveling area.
Generally, an electromagnetic induction automated guided vehicle automatically traveling on a specified traveling road along an induction line by detecting an induction signal outputted from an induction line previously laid on the road surface (Japanese Patent Application Publication No. 4-67641), and an automatic driving system for vehicles driving a guided vehicle based on an amount of relative displacement between a white line laid on a road and the guided vehicle which is detected by a CCD camera (Japanese Patent Application Laid-open No. 4-27331) are known to be used as an automatic driving system of an automated guided vehicle.
Since laying an induction line on the entire traveling reference line is restricted by cost and has many inconveniences, such as trouble of a broken line and so on caused by vehicles and so on traveling on the induction line, a system is proposed which travels and is induced by bodies as detecting signs consisting of magnets which are embedded at specified intervals on the traveling reference line (Japanese Patent Application Laid-open No. 3-177905). A traveling route in which a magnet is embedded with a specified interval provided is formed and a sensor for calculating displacement by detecting magnetism of each magnet is attached on a vehicle body. An azimuth sensor is provided on the vehicle body, and by calculating the deviation from azimuth information previously set between adjacent magnets, the vehicle automatically travels along the route to its goal.
Incidentally, for an automatically traveling automated guided vehicle, when moving along the traveling route prescribed in the above, it is important to take a measure such as an automatic halt and so on when the existence of an obstacle is recognized on a traveling route, and to this end, an obstacle detection sensor is provided. As sensors of this kind, a method for radiating a ultrasonic wave and a method for radiating a millimeter wave are conventionally known, however they have disadvantages of low responsiveness resulting in detecting an obstacle at only one point and being unable to detect human beings, of low sensitivity in rainfall and snowfall, and of catching noise and so on. Therefore, recently there has been a tendency to use an obstacle detection sensor using a laser beam for reasons of having high resolution at a long distance with high directivity and surely detecting human beings. Such a laser sensor radiates a laser beam projected from the light source in a side direction of the vehicle, then detects the reflected light from an obstacle in the range of a traveling route and calculates the distance to determine when to halt the vehicle and so on in accordance with the extent of the distance to the obstacle. The conventional laser obstacle detection sensors are provided with a light sending and receiving window at the casing for projecting a laser beam from the window to the outside through a light projecting mirror, and for detecting the reflected light from the same window through a half mirror. The reflected light is input to a photoelectric element, and the time from the radiation to the reception of the reflected light is calculated to calculate the distance. In order that precipitation such as raindrops are not detected as an obstacle, a method for detecting reflected light intensity is adopted, and generally only a signal with a reflection intensity greater than a specified threshold is detected as an obstacle.
However, in the conventional laser obstacle detection sensor, there is a disadvantage of being unable to surely prevent misdetection of raindrops as a ghost obstacle at rainfall, though a method for detecting an obstacle only when reflected light with intensity more than a specified level is detected especially from a viewpoint that reflected light intensity from raindrops is small. On the window forming the laser beam projecting portion and receiving portion, a light transmittable protective plate such as acrylic resin or the like is attached and there are disadvantages of detecting the vehicle itself equipped with the sensor being detected as an obstacle and of mistakenly recognizing reflected light from contacting water drops which are directly received when raindrops and so on contact this protective plate. Further, in an automated guided vehicle or the like requiring a sensor of this kind, the inclination of a vehicle body caused by partial loading, or the detection of the ground surface as an obstacle due to the vibration during traveling occur, and these things empirically occur especially in rainfalls.